The present invention relates to a magnetic disk apparatus, and in particular to a magnetic disk apparatus that includes a shroud disposed surrounding the outer periphery of a recording disk.
In a magnetic disk apparatus, an air current arises inside the casing as a result of a recording disk rotation. This air current revolves in the same direction as the recording disk in the vicinity of the surface of the recording disk, and proceeds to the outer side due to centrifugal force. Part of the current returns after it passes through a gap between the outer peripheral surface of the recording disk and the shroud surface and reaches the other side, and becomes a serpentine current in the gap by repeatedly passing through the gap. The recording disk is excited by the difference in pressure between the upper and lower surfaces of the disk arising as a result of the serpentine current, which results in the disk fluttering.
To counter this problem, JP-A-2000-322870 (Patent Document 1) discloses a structure where a protrusion is disposed across the substantial entire periphery of the shroud, and this convex portion enters the space between the recording disks. Thus, the serpentine current passing through the interval is deterred and disk fluttering is suppressed.
JP-A-2000-348465 (Patent Document 2) discloses suppressing disk fluttering by setting the distance between the outer peripheral surface of the recording disk and the shroud surface facing the outer peripheral surface of the recording disk to 0.5 mm or less, and disposing a rectifying groove along the substantial entire periphery of the shroud adjacent to the region of the shroud facing the outer peripheral surface of the recording disk.